A known push-button switch of this kind is shown in FIG. 1, and is comprised of a casing 1 having an open lower end with a printed circuit board 2 serving as the base of the switch. A stem 3 extends through the top wall of the casing 1, and a block 4 of sponge material is fixedly secured to the inner end of the stem 3. A circular movable contact 5 is firmly fixed to the lower end of the block 4 of the sponge, and fixed contacts 6 and 7 are disposed on the printed circuit board 2 in a position opposite to the movable contact 5. A top cover 9 is provided over the stem 3, and a rectangular shaft 10 extends downwardly from the center of the top cover 9 into a recess 8 of the stem 3. An elastomeric cylinder 11 of rubber or the like is disposed between the casing 1 and the top cover 9 and is loosely mounted on the periphery of the stem 3. The cylinder acts to bias the stem 3 upwardly when depressed. The casing 1 is rigidly fixed to the printed circuit board 2.
In the operation of the conventional push-button switch constructed as described above, when the top cover 9 is depressed against the resilience of the cylinder 11 of rubber, the stem 3 is shifted downward to cause the movable contact 5 to bear on the fixed contacts 6 and 7, thus closing the circuit. When the depressing force exerted on the cover 9 is released, the resilience of the rubber cylinder 11 restores the top cover 9 to its original state. At the same time, the movable contact 5 is disengaged from the fixed contacts 6 and 7, whereby the circuit is opened.
In the prior art push-button switch as mentioned above, a gap of dimension a may be produced between the top cover 9 and the rubber cylinder 11 while the switch is being assembled. In this case, the cylinder 11 is free to move vertically and from side to side, creating an undesirable situation.
In an attempt to remove this difficulty, another push-button switch shown in FIG. 2 has been proposed. The rubber cylinder 11 of this switch is provided with a flange 11a around its lower end, and the flange 11a is retained by a claw 12 mounted on the top end of the casing 1. This switch is capable of preventing the rubber cylinder 11 from vibrating up and down or from moving side to side, but it has a complicated shape resulting in increases in production efficiency.